Methods of enhancing dyeability of polymers

ABSTRACT

The invention relates to new methods of dyeing polymers. The methods include dispersing nanomaterials into the polymers to form polymer nanocomposites, and dyeing the polymer nanocomposites with a dye. The invention also relates to dyed polymers thus obtained and articles made from these dyed polymers.

TECHNICAL FIELD

[0001] This invention relates to methods of dyeing polymers, morespecifically, methods of enhancing the dyeability of polymers.

BACKGROUND

[0002] Dyeing polymers such as polyolefins (e.g., polypropylene) hasbeen a challenge to polymer and textile chemists for many decades.Currently available approaches rely mainly on copolymerization,polyblending, grafting, and plasma treatment technologies. Examples ofsuch polymers include vinylpyridine/styrene copolymers;poly(ethylene/vinyl acetate) blended with polypropylene for dispersedyeability; stearyl methacrylate, dimethylaminopropylacrylamide, orbasic imidized styrene-maleic anhydride copolymer for acid and dispersedyeability; stearyl methacrylate-maleic anhydride for basic and dispersedyeability; and organo-metal-complexes for specially selected dyes. See,e.g., Akrman et al, Journal of the Society of Dyers and Colourists, 114,209-215 (1998); Luc et al., International Dyer, 32-36 (1998); and U.S.Pat. Nos. 6,127,480, 6,039,767, 5,985,999, 5,576,366, 5,550,192, and5,468,259.

[0003] One disadvantage of these technologies is that they considerablyincrease the costs of the dyed products due to the cost increase of theprocess and materials. Another disadvantage is that some of thesetechnologies are not suitable for producing fine fibers used in clothingmaterials.

SUMMARY

[0004] The invention is based on the discovery that the dyeability ofpolymers, such as polyolefins, can be significantly enhanced byincorporating into the polymers a nanomaterial such as a nanoclay,nanosilica, metal oxide (e.g., zinc oxide, silver oxide, calcium oxide,platinum oxide), zeolite, or nanoparticles of polymers (e.g.,polysiloxanes). The term “dyeability” refers to a polymer's ability tobe dyed, the rate at which the polymer can be dyed, the amount of dyethat can be applied to the polymer (i.e., dye exhaustion), and thefastness of the dyes on the dyed polymers.

[0005] Accordingly, the invention is related to methods of dyeingpolymers by first dispersing a nanomaterial into the polymer to form apolymer nanocomposite, and then dyeing the polymer nanocomposite with adye.

[0006] A “nanomaterial” refers to a particulate inorganic or organiccompound or composition having a particle size in the range of 1-1,000nm (e.g., 50-200 nm or 200-600 nm). Nanomaterials thus include nanoclay,nanosilica, metal oxides (e.g., zinc oxide, silver oxide, calcium oxide,or titanium oxide), zeolites, and nanoparticles of a polymer.Nanomaterials can be pretreated with ionic surfactants (e.g., alkylammonium salts or fluoro-organic compounds) for enhanced compatibilitywith the polymer (e.g., enhanced hydrophilicity, hydrophobicity, oramphiphilicity, depending on the hydrophilicity or hydrophobicity of thepolymers), and subsequent improved (i.e., more even) dispersion,depending on the polymers.

[0007] The new methods are applicable to all polymers that need to bedyed including those polymers that may be difficult to dye using knowntechniques. Such polymers include polyvinyls (e.g., polystyrene), epoxyresins, polyolefins (e.g., polypropylene), polyamides (e.g., nylon 6),aromatic polyamide (e.g., aramid), polyimides (e.g.,polypyromellitimide), polyanhydrides (e.g., polymaleic anhydride),acrylic polymers (e.g., polymethyl methacrylate), polyesters (e.g.,poly(ethylene terephthalate)), polyimines (e.g., polyethyleneimine),polysaccharides (e.g. rayon), polypeptides (e.g., zein), polylactones(e.g., polycaprolatone), and their random or block copolymers. Usefulpolymers also include derivatives of polymers, e.g., polymers with esterderivatives on side acidic groups. The molecular weights of the polymerscan be in the range of 15,000 to 150,000, and they can be amorphous orhighly crystalline.

[0008] The methods are particularly suitable for polymers which aredifficult to dye. Such polymers, which generally have no or very limiteddyeability, include polyolefins, polyvinyls, aromatic polyamides, andepoxy resins.

[0009] Embodiments of the new methods include those in which thepolymers are polyvinyls, epoxy resins, polyolefins, polyamides, aromaticpolyamides, polyimides, polyanhydrides, acrylic polymers, polyesters,polyimines, polysaccharides, polypeptides, polylactones, or a random orblock copolymers thereof; and those in which the weight ratio of thenanomaterial to the polymer is in the range of 0.01-20% (e.g., 0.1-10%or 0.5-5%).

[0010] The polymer nanocomposites thus obtained can be in the form offibers, films, membranes, tubes, or particles.

[0011] The invention also relates to novel dyed polymer nanocomposites,each containing dye molecules, a polymer, and a nanomaterial dispersedin the polymer. The dyed polymer nanocomposites can be prepared by firstobtaining polymer nanocomposites and then dyeing the polymernanocomposites.

[0012] Also within the scope of the invention are articles made of thenovel dyed polymer nanocomposites.

[0013] Unless otherwise defined, all technical and scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which this invention belongs. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of the present invention, suitable methods andmaterials are described below. All publications, patent applications,patents, and other references mentioned herein are incorporated byreference in their entirety. In case of conflict, the presentspecification, including definitions, will control. In addition, thematerials, methods, and examples are illustrative only and not intendedto be limiting.

[0014] The new methods and dyed polymers provide numerous advantages.For example, the methods are relatively inexpensive and easy to carryout. In addition, the dyed polymers can be easily processed and haveexcellent mechanical strength, tensile strength, gas impermeability,flame retardance, and heat resistance. The dyeability of the resultantnanocomposites (e.g., dye exhaustion rate and colorfastness) can beengineered based on the selection of the nanomaterials and themodification of the process.

[0015] The details of several embodiments of the invention are set forthin the description below. Other features, objects, and advantages of theinvention will be apparent from the description and drawings, and theaccompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a graph showing build-up curves of an acid dye inpolypropylene nanocomposites.

[0017]FIG. 2 is a graph showing build-up curves of a disperse dye inpolypropylene nanocomposites.

[0018]FIGS. 3A to 3D are illustrations of a polypropylene nanocomposite(nanoPP1) dyed in different dye bath concentrations, each containing anacid dye. The amount of dye build-up in the composite increased with anincrease of the depth of shade in the dye bath.

[0019]FIGS. 4A to 4C are illustrations showing another polypropylenenanocomposite (nanoPP3) dyed in different dye bath concentrations, eachcontaining a disperse dye. The amount of dye build-up increased with anincrease of the depth of shade in the dye bath.

[0020]FIGS. 5A to 5D are illustrations showing another polypropylenenanocomposite (nanoPP6) dyed in different dye bath concentrations, eachcontaining a disperse dye. The amount of dye build-up increased with anincrease of the depth of shade in the dye bath.

[0021]FIGS. 6A to 6D are illustrations showing another polypropylenenanocomposite (nanoPP7) dyed in different dye bath concentrations, eachcontaining a disperse dye. The amount of dye build-up increased with anincrease of the depth of shade in the dye bath.

DETAILED DESCRIPTION

[0022] The present invention provides methods of enhancing thedyeability of a wide variety of polymers, such as polyvinyls (e.g.,polystyrene), epoxy resins, polyolefins (e.g., polypropylene),polyamides (e.g., nylon 6), aromatic polyamide (e.g., aramid),polyimides (e.g., polypyromellitimide), polyanhydrides (e.g., polymaleicanhydride), acrylic polymers (e.g., polymethyl methacrylate), polyesters(e.g., poly(ethylene terephthalate)), polyimines (e.g.,polyethyleneimine), polysaccharides (e.g. rayon), polypeptides (e.g.,zein), polylactones (e.g., polycaprolatone), and their random or blockcopolymers. The methods include forming nanocomposites of these polymersby using a nanomaterial, e.g., nanoclay (which contains montmorillonite(MMT) Al₂Si₄O₁₀(OH)₂), nanosilica, metal oxide, zeolite, ornanoparticles of polymers such as polysiloxanes.

[0023] Preparation of Polymer Nanocomposites

[0024] The methods include first selecting a suitable nanomaterial whichis optionally treated with a surfactant (e.g., an anionic or cationicsurfactant such as an alkyl ammonium salt) to modify its surface. Afterthe surface modification, the nanomaterial can become hydrophilic,hydrophobic, or amphiphilic, thereby enhancing the accessibility of dyemolecules to the polymer nanocomposite. A polymer (e.g., a polyolefin),optionally dispersed (e.g., intercalated, or exfoliated) with a certainamount of the nanomaterial is then heated to melt, or is dissolved in anorganic solvent, which is optionally heated. The nanomaterial is thendispersed into the molten polymer or the polymer solution, giving apolymer nanocomposite. Even dispersion of the nanomaterial in thepolymer or polymer solution can be achieved by methods known in the art,e.g., by continuous stirring, ultrasonication, and/or compounding (e.g.,extrusion), optionally with the aid of additional surfactants.

[0025] The dispersion of the nanomaterials within the polymers createsdye sites for dyeing the polymers. Prior to the dispersion, othercomponents (e.g., fillers, which are water insoluble solids) can also beadded into the melted polymers or polymer solutions. The othercomponents can be added directly (i.e., as solids) to the meltedpolymers or the polymer solutions. These other components can also beadded as solutions in organic solvents. Additional examples of the othercomponents include plasticizers, different types of polymers, or otheragents as needed.

[0026] The dispersion of the nanomaterials in the polymers can becontrolled, e.g., by changing the duration, pulse, and amplitude of theultrasonication, the crystallinity of the polymer, or the compatibilityof the nanomaterial and polymer. For instance, better dispersion (e.g.,more even distribution of the nanomaterials in the polymers) can beachieved by increasing the duration or amplitude of the pulse of theultrasonication. Under the same conditions, nanomaterials can be betterdispersed into polymers that are more crystalline. Better dispersion canalso be achieved in nanocomposites that contain nanomaterials andpolymers that are more compatible (e.g., hydrophilic nanomaterials andhydrophilic polymers) than in nanocomposites that contain lesscompatible nanomaterials and polymers (e.g., hydrophilic nanomaterialsand hydrophobic polymers).

[0027] After the dispersion, the melted polymers or the polymersolutions can be allowed to solidify for storage or further processing.They can also be directly processed into a desired form, e.g., film,fibers, particles, or cylinders, using standard techniques.

[0028] The polymer nanocomposites thus obtained can be characterized bymethods known in the art. For instance, their thermal properties can bedetermined by using Differential Scanning Calorimetry (DSC). Aninjection molder can be used for mechanical testing and for measuringthe nanocomposites' dynamic moduli. See, e.g., Hasegawa et al., J.Applied Poly. Sci., 67, 87-92, 1998. The dispersity of the nanomaterialin the polymer can be evaluated by using wide-angle X-Ray Diffraction(XRD) and Transmission Electron Microscopy (TEM). See, e.g., Manias etal., Polymeric Materials, Science & Engineering, 82, 282-283, 2000.Optical microscopy studies can reveal how the polymer nanocomposites aredyed. Tests of the tensile strength of the polymer nanocomposites can becarried out with an Instron tensile tester.

[0029] Because of their mechanical strength, the polymer nanocompositescan be used as bulk materials, e.g., for packaging. They can also bemade into fibers that can be used to manufacture woven or non-wovenfabrics.

[0030] Dyeing the Polymer Nanocomposites

[0031] The polymer nanocomposites obtained as described above can bedyed using conventional methods. For instance, they may be dyed in a dyebath using conventional ionic dyes (i.e., acid or basic dyes) anddisperse dyeing techniques.

[0032] Acid dyes (one type of anionic dyes) contain acidic groups, suchas —SO₃H, and are used with polymer nanocomposites containing basicgroups that can interact with these acidic groups. The most commonstructural types of acid dyes are monoazo and anthraquinone dyes.Examples of acid dyes include C.I. (Color Index) Acid Red 138, C.I. AcidRed 266, and C.I. Acid Blue 45. Structures of these three dyes are shownbelow:

[0033] Basic dyes (also called cationic dyes) can be used for dyeingpolymer nanocomposites that carry anionic groups. Examples of basic dyesinclude C.I. Basic Blue 3 and C.I. Basic Green 4, with structures shownbelow:

[0034] Disperse dyes are nonionic and almost insoluble in water. Theyare used as finely distributed aqueous dispersions. Like acid dyes, thetwo most common types of disperse dyes are also monoazo andanthraquinone dyes. Examples of disperse dyes include C.I. Disperse Blue183 and C.I. Disperse Blue 73, with their structures shown below:

[0035] Additional ionic (i.e., acid and basic) and disperse dyes usefulin the new methods are listed in “Dyes and Pigments by Color Index andGeneric Names” in Textile Chemist and Colorist, 24 (7), 1992.

[0036] Generally, the dye is used in the form of a dye solution so thatit can be readily applied by dipping the polymer nanocomposites into acontainer with the dye solution, by spraying the dye solution onto thepolymer nanocomposites, or by using a cascading roll technique. The dyesolution can also be in the form of a print paste, which is typicallyused in roller printing or screen printing, particularly on fabrics madefrom the polymer nanocomposites. The polymer nanocomposites can be dyedmultiple times using one or more dyeing techniques.

[0037] Aqueous dye baths typically have a pH value in the range fromabout 2 to about 11, e.g., from about 2.5 to about 6.5 for acid dyes,from about 8.5 to about 10.5 for reactive dyes, and from about 4.5 toabout 6.5 for disperse dyes and basic dyes. The pH may be adjusted, ifdesired, using a variety of compounds, such as formic acid, acetic acid,sulfamic acid, citric acid, phosphoric acid, nitric acid, sulfuric acid,monosodium phosphate, trisodium phosphate, sodium carbonate, sodiumbicarbonate, ammonium hydroxide, sodium hydroxide, or a combinationthereof. A surfactant, typically a nonionic surfactant, can also be usedto aid in dispersing sparingly water-soluble disperse dyes in a dyebath. During the dyeing step, the dye bath is agitated to hasten thedyeing rate. The dyeing step can be carried out at a variety oftemperatures, with higher temperatures generally promoting the rate ofdyeing.

[0038] The polymer nanocomposites can also be dyed by jet dyeing (seeEngineering in Textile Coloration edited by C. Duckworth, p. 56, DyersCompany Publications Trust, 1983), which permits high-temperature dyeingand impingement of the dye onto moving polymer nanocomposites (typicallyin the form of fabrics) through use of a venturi jet system. Dyecarriers permit faster dyeing of the polymer nanocomposites, e.g., atatmospheric pressure and below 100° C. Such dye carriers are typicallyorganic compounds that can be emulsified in water. Representativeexamples of such carriers include aromatic hydrocarbons such as diphenyland methylnaphthalene, phenols such as phenylphenol, chlorinatedhydrocarbons such as dichloro- and trichloro-benzene, and aromaticesters such as methyl salicylate, butyl benzoate, diethylphthalate, andbenzaldehyde. These carriers usually can be removed from the dyedmaterials after dyeing. Dye carriers increase the rate of dyeing byaffecting both the polymer and the dye bath. The absorption of typicalcarrier substances alters the viscoelastic properties of the polymernanocomposite in a manner consistent with the view that carrier activityis associated with an increase in polymer segmental mobility, at leastin the more accessible region of the polymer chain molecules. Inaddition to the use of carriers in promoting the build-up of dyeing atthe boil, small amounts of carriers may be added in high-temperaturedyeing processes to promote the leveling of the more difficult dispersedyes.

[0039] During dyeing, the dyes are first adsorbed onto the surface ofthe polymer nanocomposites, and subsequently attracted to the dye sitescreated by the dispersion of the nanomaterials. Ultimately, the dyemolecules attach themselves to the nanocomposites, thereby enhancing thedyeability of the polymer nanocomposite. In some applications (e.g.,thermosol dyeing), dry heat may be applied to the polymer nanocomposites(after they are removed from the dye baths) at a wide range of elevatedtemperature to cause the dye to penetrate into, and become fixed in, thepolymer nanocomposites. The dye fixation step involves exposing the dyedpolymer nanocomposites to high temperature, wet or dry, e.g., in anoven. The temperature can vary up to 20 or 25° C. below the meltingtemperatures of the polymer nanocomposites. Generally, higher dryingtemperatures result in shorter drying times. Typically, the heating timeis from about 1 minute to about 10 minutes. Residual dyes may then beremoved from the polymer nanocomposites, e.g., by rinsing with water ora reduction-clearing bath.

[0040] Characterization of the Dyed Polymer Nanocomposites

[0041] A dyed polymer nanocomposite can be characterized, e.g., bymeasuring the affinity between the dye and the polymer. The dyeabilitycan also be evaluated by determining the percentage exhaustion of thedye in a dye bath, e.g., by measuring the absorbance of the dye bath atthe beginning and after dyeing, by using a spectrophotometer.

[0042] The fastness against light, washing, rubbing, shampooing, and drycleaning of the novel dyed polymer nanocomposites can be evaluatedaccording to ISO procedures (e.g., ISO-B02:1994, ISO 105-CO1:1989, ISO105-X12:1992, ISO document 473, and ISO 105-DO1:1993, respectively).

[0043] The efficiency of dyeing (i.e., dyeability) depends on the typeof dye and polymer, the size and structure of the nanomaterial, and theweight ratio of the nanomaterial to the polymer. A higher efficiency ofdyeing can be achieved by adding a higher amount of the nanomaterialinto the polymers when the other factors (i.e., the types of the dye andthe polymer, and the size and structure of the nanomaterial) are thesame. In general, the higher the compatibility between the nanomaterialand the polymer, or the lower the crystallinity of the polymer, thehigher the dyeability of the polymer nanocomposite.

[0044] On the other hand, more even dyeing (improved color yield) can beachieved in nanocomposites in which the nanomaterials are more evenlydistributed within the polymers. It can also be achieved when a dye ofsmaller size is used.

[0045] Uses of the Dyeable Polymer Nanocomposites

[0046] The new dyeable polymer nanocomposites have improved mechanicalproperties and tensile strength, and low permeability. Further, when theamount of a nanomaterial is within a certain range (e.g., less than 5%),the polymer nanocomposites are also easy to process. Thus, these newdyeable polymer nanocomposites can be widely used for making fibers,fabrics, films, plates, sheets, and bulk materials such as toys,utensils, appliances, furniture, and plastic tools as well as packagingmaterials.

[0047] The invention is further described in the following examples,which are only illustrative and do not in any way limit the scope of theinvention described in the claims.

EXAMPLES Example 1:

[0048] Preparation of Polypropylene Nanocomposites with Nanoclays byUltrasonication

[0049] Isotactic polypropylene chips (Philips Sumika PolypropyleneCompany, Houston, Tex.), xylene (J.T Baker Company, Philipsburg, N.J.),and a nanoclay (Cloisite 15A, Southern Clay Company, Gonzales, Tex.)were mixed in a stainless steel container. The nanoclay contains anatural montmorillonite (MMT) modified with a quaternary ammonium salthaving a structure shown below:

[0050] wherein HT in the formula specifies hydrogenated tallow of C₁₈(approx. 65%), C₁₆ (approx. 30%) and C₁₄ (approx. of 5%).

[0051] Other specifications for Cloisite 15A, as provided by themanufacturer, are shown in Table 1. TABLE 1 Physical properties ofCloisite 15A Particle Size Color Less than 10% Less than 50% Less than90% Density, g/cc Off 2μ 6μ 13μ 1.66 White

[0052] The container was placed in a sand bath insulated by glass-fiberfabrics. A thermocouple probe was tucked in the sand bath to check thetemperature. The transducer of an ultrasonic homogenizer (750 W) wasimmersed in the stainless steel container.

[0053] This system was heated on a hot plate and the temperature wasgradually increased to the boiling point of xylene (130-140° C.) atwhich the polypropylene started to dissolve.

[0054] The ultrasonic homogenizer was started for a set period of time.The pulsation rate (i.e., the time for which the ultrasonic is ON andOFF) and the amplitude of the ultrasonic waves were pre-set before thestart of ultrasonic action as indicated in Table 2 below. Thetemperature was maintained in the range of 130-140° C. during thesonication time. In some cases, a controlled amount of xylene was addedduring the homogenization process to prevent the nanocomposite fromsolidifying. After this homogenization process, the ultrasonic devicewas switched off and the transducer was removed. The remaining xylenewas allowed to evaporate at its boiling temperature until the polymernanocomposite solidified.

[0055] Table 2 shows the detailed specifications of the nanocomposites(owp stands for on weight (or by weight) of polypropylene): TABLE 2Composition of nanoclay polypropylene (PP) nanocomposites Weight Ultra-of sonic Ampli- Sample Nanoclay Xylene (g), PP time Pulse tude ID (g), %owp % owp (g) (min) (s) (%) PP0 — 40 g, 500%  8 g 20 3 on 50% 5 offnanoPP1  0.4 g, 5% 40 g, 500%  8 g 7 3 on 50% 5 off nanoPP2  0.6 g, 20%60 g, 2000%  3 g 15 3 on 70% 3 off nanoPP3  0.3 g, 2% 50 g, 500% 15 g 303 on 70% 3 off nanoPP4 0.75 g, 5% 50 g, 500% 15 g 30 3 on 70% 3 offnanoPP5 0.75 g, 5% 30 g, 200% 15 g 30 con- 70% tin- uous nanoPP6 1.50,10% 75 g, 500% 15 g 15 3 on 70% 3 off

Example 2:

[0056] Dyeing the Nanoclay Polypropylene Nanocomposites

[0057] The nanoclay polypropylene nanocomposites prepared in Example 1were molded into films by using a hot laboratory press, which was heatedto the melting point of the nanoclay polypropylene nanocomposites (i.e.,170° C.), to obtain very fine, thin layers of the polypropylenenanocomposites.

[0058] The nanoclay polypropylene nanocomposite films thus obtained weredyed in an aqueous dye bath containing an acid dye C.I. Acid Red 266, oran aqueous dye bath containing a disperse dye C.I. Disperse Red 65.

[0059] Acid Dyeing

[0060] Aqueous dye baths containing 1, 2, and 4% by weight of C.I. AcidRed 266 (i.e., 1, 2, and 4% depth of shade) were first prepared. The pHof the dye bath was 3.5. For even dyeing, the dye bath also contained ananionic leveling agent, Orco Nyasol Leveler AA-50, at a concentration of10 g/l.

[0061] Into each of these dye baths was added a polypropylenenanocomposite film described above at a weight ratio of 1:20 (polymernanocomposite: dye bath). The dyeing process was conducted in AhibaPolymat Laboratory dyeing machine.

[0062] The dye bath was heated in a sealed stainless steel dyeing with atemperature increase from 30C. to 100° C. at a rate of 2° C./minute. Thetemperature was then kept constant for 60 minutes. Finally the dye bathwas cooled to 40° C. The samples were extracted and washed with coldrunning water for 5 minutes.

[0063] Disperse Dyeing

[0064] Aqueous dye baths containing 1, 2, and 4% (by weight) of C.I.Disperse Red 65 were prepared. The dye baths had pH values that wereweakly acidic. The dye baths further contained, as auxiliaries, 80%acetic acid at a concentration of 1 g/l, Irgasol DAM (a dispersingagent) at a concentration of 2 g/l, and Albatex FFC (a leveling agent)also at a concentration of 2 g/l.

[0065] The polypropylene nanocomposite films were placed into the dyebaths, also at a weight ratio of 1:20. The dyeing process was conductedin an Ahiba Polymat Laboratory dyeing machine.

[0066] Dyeing was performed by raising the dye bath temperature from 40to 130° C. at 1.5° C./minute, holding at this temperature for 45minutes, and cooling to 60° C. at 3° C./minute. The dyed polymernanocomposite films were rinsed in running water for 5 minutes with handagitation. Reduction clearing was done by placing the dyed films for 10minutes at 60-70° C. in a solution containing 6 ml/l 30% caustic sodaand 4 g/l hydrosulfite at a weight ratio of approximately 1:40 (dyedpolymer nanocomposite:solution). The samples were then rinsed for atleast 5 minutes with cold (15-25° C.) running water. Finally, the dyedpolypropylene composite films were neutralized with 1.2 ml/l 99.9%acetic acid for 2 minutes and then rinsed with cold (15-25° C.) runningwater for at least 5 minutes.

Examples 3:

[0067] Preparation of Silica Polypropylene Nanocomposites

[0068] An organo silica dispersed in methyl ethyl ketone (MEK) (NissanChemical Industries, Ltd., Tarrytown, N.J.) was used to prepare a silicapolypropylene nanocomposite following the procedure described inExample 1. Specifications of the silica and the composition of thesilica polypropylene nanocomposite are listed below in Tables 3 and 4,respectively: TABLE 3 Physical properties of silica SiO₂ Water Particlesize Viscosity Dispersant (wt %) (wt %) (nm) S. Grav. (mPa · s) MEK 30<0.6 10-20 0.98 <5

[0069] TABLE 4 Composition of PP nanocomposites Ultra- weight sonicAmpli- weight of os xylene (g), of time Pulse tude Sample (g), % owp %owp PP (g) (min) (s) (%) nanoPP6 1.50, 10% oc  75 g, 500% 15 g 15 3 on70% 3 off nanoPP7  2.5, 5% oc 250 g, 500% 50 g 30 3 on 70% 3 off

Example 4:

[0070] Dyeing of Silica Polypropylene Nanocomposite

[0071] The silica polypropylene nanocomposite obtained from Example 3was molded into film by using a hot laboratory press heated to 185° C. Asquare template was placed between the jaws of the press. For an eventhickness, the films were removed when the temperature of the presscooled down to 80° C.

[0072] The silica polypropylene nanocomposite films thus obtained weredyed in an aqueous dye bath containing an acid dye C.I. Mordant Black17, or an aqueous dye bath containing a disperse dye C.I. Disperse Blue102. The acid dye bath and the disperse dye bath were of the samecompositions and concentration as those described in Example 2, exceptthat the dyes were different.

Example 5:

[0073] Dyeing of Polypropylene Films

[0074] For comparison, films of virgin polypropylene (i.e., propylenewithout any modifications) were prepared and dyed according to theprocedures described in Example 1 and Example 2.

Example 6:

[0075] Washfastness Test

[0076] Color fastness is the resistance of the color of textiles to thedifferent agents and environments to which these materials may beexposed during manufacture and their subsequent applications. The dyedpolypropylene nanocomposite films obtained in Examples 2 and 4, and thedyed polypropylene films obtained in Example 5, were tested for theirfastness against washing by the following procedure:

[0077] A wash solution was first prepared by dissolving 4 g of AATCC(the American Association of Textile Chemists and Colorists) standarddetergent WOB in 1 liter of distilled water. The dyed film samples werethen put into the test container and 50 ml of the above washing solutionwas added. After the lid of the container was secured, theLaunder-ometer (Atlas Electric Devices, Co., Chicago, Ill.) was allowedto run for 30 minutes at 60° C. Upon completion, the dyed film sampleswere rinsed twice for 1 minute in water at 40° C. The rinsed sampleswere subject to visual, spectral, and microscopic (SEM) analysis.

[0078] The results show that dispersion of a nanomaterial into thepolypropylene increased its dyeability as compared to the virginpolypropylene, which was not dyeable with an acid dye and was only dyedto a very low extent with a disperse dye. Varying the quantity ofnanomaterials in the nanocomposites had a noticeable effect on theexhaustion of the dye.

[0079] The results further show that nanocomposites containing higheramounts of nanomaterials are dyed more evenly than those containinglower amounts of nanomaterials. For instance, nanoPP1, nanoPP4, andnanoPP5 (all of which were prepared with 5% add-on of nanoclay) hadimproved color yield (i.e., more even dyeing) as compared to nanoPP3(which was prepared with 2% add-on of nanoclay). The comparison of K/S(Kubelka-Munk coefficient) values at 2% depth of shade indicates thatnanoPP1 (5% nanoclay add-on) had a slightly better color yield thannanoPP3 (2% nanoclay add-on) when they were dyed with a disperse dyebath at 4% depth of shade. NanoPP2 (20% nanoclay add-on) dyed with acidand disperse dye baths also showed much more even dyeing than nanoPP3and nanoPP4 (2% and 5% nanoclay add-ons, respectively).

[0080] A longer duration of ultrasonication also results in a more evendye distribution. In the case of acid dyeing, a comparison between dyednanoPP1 (7 minutes) and dyed nanoPP4 (30 minutes) showed that the dyehad exhausted more on dyed nanoPP4 than nanoPP1.

[0081] The nature of the build-up curves, among other factors, wasinfluenced by the chemical structure of the dye and the available dyesites in the nanocomposites. The build-up curves were also affected bythe depth of shade (i.e., dye concentration) in the dye bath. As shownin FIG. 1 and FIG. 2, there is an increase in the color yield from 1 to4% depth of shade except for nanoPP1 and nanoPP5 where the curve isalmost flat from 2 to 4% depth. This, however, may be related to theunavailability of dye sites (nanoclay) in proportion to the amount ofdye in the dyebath. This effect was observed in all the nanocompositesamples that were disperse dyed. In other words, the disperse dye onpolypropylene nanocomposites reaches saturation at higher dyeconcentration. However, high color yield on disperse dyed samples wasobserved with increased concentration of dyes without a noticeabledifference between the dyed nanocomposites with varying amount ofnanoclay.

[0082] The results also indicate that dye exhaustion increased with theincrease of depths of shades of dye baths. As shown in FIGS. 3A-3D,4A-4C, 5A-5D, and 6A-6D, the dye exhaustion increased with the increaseof the depths of shades in dye baths, i.e., 1% to 4%, in all the testednanocomposites.

Example 7:

[0083] Lightfastness Test The fabrics and polypropylene nanocompositefilms are cut into the dimension of 70×120 mm. The specimens are thenstapled on the white card and one part of the sample is exposed (55×25mm) which is called the 20-hour sample. The white cards with the samplesare mounted on the frames. The fading apparatus is arranged by clampingone full (cored) and another half (solid) carbon electrodes andenclosing them in a glass bulb. A Fade-ometer (Atlas Electric Devices,Co., Chicago, Ill.) is set to the operating conditions specified in theAATCC Test Method 16-Option A. The specimen rack is filled with theframed white cards and the required black thermometer unit. A thermostatis used to maintain the chamber temperature to the test specifications(63° C.). The chamber drum is filled with water to maintain the requiredvalue of humidity (30%). The timer is adjusted and the machine is runfor 20 hours after which it stops automatically. The frames (withsamples) are removed and the exposed area is compared with the unexposedpart of the sample. The samples are evaluated according the AATCC GrayScale Rating.

Example 8:

[0084] Dyeing Nanocomposites of Polyacrynitrile

[0085] Nanocomposites of polyacrylnitrile are prepared and dyedaccording to the procedures described in Examples 1 and 2, except thatN,N-dimethylformamide (DMF) is used, instead of xylene.

OTHER EMBODIMENTS

[0086] It is to be understood that while the invention has beendescribed in conjunction with the detailed description thereof, theforegoing description is intended to illustrate and not limit the scopeof the invention, which is defined by the scope of the appended claims.Other aspects, advantages, and modifications are within the scope of thefollowing claims.

What is claimed is:
 1. A method of dyeing a polymer, the methodcomprising dispersing a nanomaterial into the polymer to form a polymernanocomposite, and dyeing the polymer nanocomposite with a dye.
 2. Themethod of claim 1, wherein the polymer is a polyvinyl, epoxy resin,polyolefin, polyamide, aromatic polyamide, polyimide, polyanhydride,acrylic polymer, polyester, polyimine, polysaccharide, polypeptide,polylactone, or a random or block copolymer thereof.
 3. The method ofclaim 1, wherein the polymer is a polyolefin.
 4. The method of claim 3,wherein the polyolefin is polypropylene.
 5. The method of claim 1,wherein the nanomaterial is nanoclay, nanosilica, metal oxide, zeolite,or nanoparticles of a polymer.
 6. The method of claim 1, wherein ananomaterial is pretreated with a surfactant for improved compatibilitywith the polymer.
 7. The method of claim 1, wherein a weight ratio ofthe nanomaterial to the polymer is in the range of 0.01-20%.
 8. Themethod of claim 1, wherein the weight ratio of the nanomaterial to thepolymer is in the range of 0.5-5%.
 9. The method of claim 1, wherein thenanomaterial is intercalated or exfoliated in the polymer.
 10. A dyedpolymer comprising a dye, a polymer, and a nanomaterial, wherein thenanomaterial is dispersed in the polymer to form a polymernanocomposite, and the dye is linked to the nanomaterial.
 11. The dyedpolymer of claim 10, wherein the polymer is a polyvinyl, epoxy resin,polyolefin, polyamide, aromatic polyamide, polyimide, polyanhydride,acrylic polymer, polyester, polyimine, polysaccharide, polypeptide,polylactone, or a random or block copolymer thereof.
 12. The dyedpolymer of claim 10, wherein the polymer is a polyolefin.
 13. The dyedpolymer of claim 12, wherein the polymer is polypropylene.
 14. The dyedpolymer of claim 10, wherein the nanomaterial is nanoclay, nanosilica,metal oxide, zeolite, or nanoparticles of a polymer.
 15. The dyedpolymer of claim 14, wherein the nanomaterial is pretreated with asurfactant for improved compatibility with the polymer.
 16. The dyedpolymer of claim 10, wherein the weight ratio of the nanomaterial to thepolymer is in the range of 0.01-20%.
 17. The dyed polymer of claim 10,wherein the weight ratio of the nanomaterial to the polymer is in therange of 0.5-5%.
 18. The dyed polymer of claim 10, wherein thenanomaterial is intercalated or exfoliated in the polymer.
 19. Anarticle made of the dyed polymer of claim 10.